Electronic controller devices (e.g., an electro-pneumatic controller, programmable controllers, analog control circuits, etc.) are typically used to control process control devices (also referred to interchangeably herein as “control devices” or “field devices,” e.g., control valves, pumps, dampers, etc.). These electronic controller devices cause a specified operation of the process control devices. For purposes of safety, cost efficiency, and reliability, many well-known diaphragm-type or piston-type pneumatic actuators are used to actuate process control devices and are typically coupled to the overall process control system via an electro-pneumatic controller. Electro-pneumatic controllers are usually configured to receive one or more control signals and convert those control signals into a pressure provided to a pneumatic actuator to cause a desired operation of the process control device coupled to the pneumatic actuator. For example, if a process control routine requires a pneumatically-actuated valve to pass a greater volume of a process fluid, the magnitude of the control signal applied to an electro-pneumatic controller associated with the valve may be increased (e.g., from 10 milliamps (mA) to 15 mA in a case where the electro-pneumatic controller is configured to receive a 4-20 mA control signal).
Electro-pneumatic controllers typically use a feedback signal generated by a feedback sensing system or element (e.g., a position transducer or a position sensor) that senses or detects an operational response of a pneumatically-actuated control device. For example, a position sensor coupled to the control device may measure the movement of an actuator of the control device, and may provide, over a wired or wireless connection, feedback indicative of the position or state of the control device to a controller of the control device.
The health and operability of process control devices, and ultimately the performance of the process system, may be adversely affected by various factors. For a control device such as a control valve assembly, for example, flow and/or component looseness may occur due to the valve moving or vibrating. Thus, to monitor the health and/or remaining service life of the control valve assembly and/or one or more components of the control valve assembly, a diagnostic device may be coupled to the control device. The diagnostic device may monitor the subject control device for movement and/or vibration, and upon detection of extraneous or excess movement or vibration, the diagnostic device may generate a warning or distress signal, which may be transmitted to the controller of the device, for example.
Known diagnostic devices typically include an accelerometer to detect the movement and/or vibration of the subject control device, and a processor that periodically or constantly queries the accelerometer to obtain current motion and/or vibration readings. As such, known diagnostic devices must continually expend energy to power the processor so that the processor may make its queries even when the motion and or vibration of the control device is within acceptable limits. Further, known diagnostic devices typically must continually expend energy to power other components as well.